Electrochemical grinding apparatus

ABSTRACT

A PROCESS AND APPARATUS FOR AUTOMATICALLY SEARCHING FOR, ESTABLISHING AND MAINTAINING ONE OR MORE SELECTED PERFORMACE PARAMETERS IN AN ELECTROCHEMICAL GRINDING OPERATION.

Oct. 10, 1972 l.. v. coLwELL ELECTROCHEMICAL GRINDING APPARATUS Filed Nov. 7, 196.8

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L. V. COLWELL ELECTROCHEMICAL GRINDING APPARATUS NS @S oct. 10,'1972 OctflO, 1972 L. v. coLwl-:LL 3,697,403 ELECTROCHEMICAL GRINDING APPARATUS Filed Nov. 7. 1968 6 Sheets-Sheet 6 CONT/COL TMI/$00666 COA/ffm,

I NVE NTOR. [5 ff aM/M United States Patent O 3,697,403 ELECTROCHEMICAL GRINDING APPARATUS Lester V. Colwell, Ann Arbor, Mich., assignor to Hammond Machinery Builders Inc., Kalamazoo, Mich. Filed Nov. 7, 1968, Ser. No. 774,009 Int. Cl. B23p 1/02 U.S. Cl. 204-218 17 Claims ABSTRACT OF THE DISCLOSURE A process and apparatus for automatically searching for, establishing and maintaining one or more selected performance parameters in an electrochemical grinding operation.

FIELD OF THE INVENTION This invention relates to electrochemical (formerly called electrolytic) grinding and relates particularly to both process and apparatus for repetitively sampling at least one selected performance parameter and from the information thereby obtained maintaining selected control parameters at values automatically to maintain at least said selected performance parameter at a desired value.

BACKGROUND OF THE INVENTION Although the basic principles of electrochemical grinding have been known for many years, and certain suggestions at least related to such grinding appear in patent and other literature as early as the middle l920s, relatively little actual commercial use of the process was made until the middle 1950s at which time there became available the teachings which eventually culminated in the U.S. patent to Keeleric No. 2,826,540. This patent sets forth empirically certain elfective operating parameters and the industry found that so long as such operating parameters were followed, at least approximately, an effective electrochemical grinding operation could be carried out. One effective machine for this purpose which has received wide commercial acceptance is described and illustrated in the U.S. patent to Bass et al., No. 2,922,258. In this machine and other machines which were developed and offered to the market in the late l950s, and which have not changed in their basic organization or operating principles up to the present time, the various operating techniques were determined and followed empirically but with little or no real understanding of the principles governing same. This approach has produced good operational results and has supplied the industry with a great amount of operating data.

However, as such operating data were accumulated and studied and attempts madel to rationalize the results obtained, it became progressively more apparent that the process is far more complex than had previously been believed and that more factors were active in influencing results than industry had previously recognized. In fact, it was discovered that in many instances, because of this incomplete understanding, machines were being operated at less than their maximum eiciency and effectiveness. Further, it was discovered that in many instances operating personnel, either because of carelessness, lack of proper instruction, or lack of attention to instruction and/ or operation, failed to operate the equipment at its maximum efficiency even where the conditions for so doing had been correctly, though empirically, determined. Since this equipment is expensive and therefore linds its primary use under conditions of high volume, repetitive, operations, it is highly important that it be operated at maximum eiciency.

The problem is often further complicated by the changing of operating conditions during the course of a normal 3,697,403 Patented Oct. 10, 1972 ice grinding procedure. For example, in the grinding of single point tools, the area being ground will change during a grinding operation and therefore require a substantial change in current flow between the grinding device (such as a wheel, belt or disk as already known) and the workpiece in order to maintain a given current density across the area being ground. Further, during a grinding operation, changes may occur in the amount of waste products accumulating on the grinding `device or in the electrolyte and thereby change the resistances resulting therefrom. All of these will require adjustment of the feed force and the current supplied to the electrochemical apparatus in order to maintain maximum efficiency but all of such advjustments are diflicult to do with optimum results with previous equipment even under laboratory conditions and with highly-skilled technicians.

At least some of these problems were recognized, and an attempt made to deal therewith, in the U.S. patent to Mittlemann, No. 3,117,919. Here the presence of arcing at a given condition of supply voltage was utilized as an indicator that the current flow had reached its maximum and was about to diminish and means sensitive to such arcing were then utilized to reduce the applied voltage to a level below that which caused such arcing. This approach, however, it not sufficiently sensitive to the many factors affecting an electrochemical operation and while a step in the right direction it was sensitive only to a single condition, namely, the occurrence of sparking, and hence it was insuiciently flexible to meet the objectives of the present invention.

It, therefore, became, and for several years has been, highly desirable to provide means by which the equipment would automatically select the optimum operating conditions for a given set of circumstances, adjust itself to, and maintain itself at, such operating conditions.

This problem, while simple to state, and while bearing some superficial resemblances to such operations as electrolytic cleaning by deplating or to the automatic control of welding current lapplied to weld pieces having varying amounts of scale or other contaminants thereon, soon proved to be exceedingly complex and subject to many previously unsuspected conditions. Accordingly, a major program of research was undertaken to determine the nature and extent of the controlling parameters and thereafter to endeavor to design equipment by which such parameters could be suitably sensed and controlled to maintain the grinding operation at a selected, usually optimum, level of effectiveness.

The results of this research has been published in a paper by applicant entitled A Physical Model of the Electro-Chemical Grinding Process presented to The American Society of Tool and Manufacturing Engineers (ASTME), in September of 1967. This paper recognizes among other things that optimum operating conditions of the electrochemical process are controlled in a complex manner by a number of parameters, such as voltage and amperage of the working current and by the feed force applied to the workpiece, but which are diicult at best to control manually. Therefore, for truly optimum operation it is strongly desirable to design apparatus for performing an electrochemical grinding process by simultaneously and automatically controlling the desired parameters to maintain the desired operating conditions.

Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words up, down, right and left will designate directions in the drawings to which reference is made. The words in and out will refer to directions toward and away from, respectively, the geometric center of the device and designated parts thereof. Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import.

The term control parameter will refer to the various controllable inputs to the electrochemical grinding apparatus, such as the voltage of the working current and the vfeeding force. The .term performance parameter will refer to relationships, either measurable or computed, to which -the control system is responsive, such as amperage of Working current, power applied to the grinding wheel for driving same, feed rate or resistance across the working gap (space between the workpiece andv the metallic surface of the grinding wheel.

The objectives of the present invention include: I

(l)v To provide a process for automatically searching for, establishing andmaintaining one or more selected performance parameters in an electrochemical grinding operation.

(2)` To provide a process for automatically sensing the operating conditions in an electrochemical grinding operation and thereafter, adjusting appropriate control para'meters to maintain the operation in a condition for obtaining ,the desired effectiveness.

(3) Tolprovideza process, as aforesaid, in which a single performance parameter, such as amperage of the working current, may be selected as indicative of other performanceparameters and used as the sole basis for controlling the operation.

(4) To provide a process, as aforesaid, in which one or more control parameters may be selected as the bases for attaining a selected combination of performance parameters and may be then controlled in a manner to attain and maintain such selected operating combination.

(5)`To provideia process, as aforesaid, in which a selected control parameter, such as applied voltage, is automatically incrementally and progressively altered from a selected beginning point toward a qualitatively known operating range, wherein a sample of a selected perfomance parameter, such as amperage of working current, is read and interpreted after each incremental adjustment of said control parameter and in which such incremental adjustment isterminated, further advanced or reversed as needed from time to time to vmaintain said performance parameter and adapted to control two con- (6) To provide a process, as aforesaid, which may be carried out by apparatus which, while in the hereinafter described preferred embodiment is sensitive to only one performance parameterv and adapaed to control two control parameters, may nevertheless be readily modifiedu Within the scope of the invention to be sensitive to a further-plurality ofperformance parameters.

(7) To provide apparatus for automatically searching for, establishing andv maintaining one or more selected performance parameters in an electrochemical grinding operation.

(8) To provide apparatus for automatically sensing a performance parameter in an electrochemical grinding operation and thereafter automatically adjusting appropriate control parameters to maintainthe operation in a condition for obtaining a selected effectiveness.

(9) To provide apparatus, as aforesaid, in which a single performance parameter, such as the amperage of the working current, may be selected as indicative of others and used as the sole basis for controlling the control parameters.

(10) To provide apparatus, as aforesaid, in which one or more control parameters may be selected as the bases for attaining a desired combination of performance parameters and may then be controlled in such a manner as to attain such operating combination.

(11) To provide apparatus, as aforesaid, in which a singlelcontrol parameter, such as the voltage of the working current, may be selected as an adequate basis for attaining the selected performance parameters and may be thencontrolled in a manner to attain and maintain such performance parameters.

12) To provide apparatus, as aforesaid, in which a selected control parameter is automatically incrementally and progressively altered from a selected beginning point toward a qualitatively known operating range, wherein a sample of a selected performance parameter is read and interpreted after each incremental adjustment of said control parameter and in which such incremental adjustment is automatically terminated, further advanced or reversed as needed from time to time to maintain said performance parameter within the operating range.

(13) To provide apparatus, as aforesaid, by which the process aspects of the invention can be carried out by a wide variety of different specificv items of equipment and can further be carried out for a variety of purposes within a variety of contexts.

(14) To provide apparatus, as aforesaid, in which, for example, the performance parameter being sensed is the working current supplied' to the workpiece and the control parameters being adjusted are the voltage at which such working current is so applied and the feed force applied to the table.

(15) To provide apparatus, as aforesaid, in which sensing means is provided for successively and incrementally changing the voltage at which the working current is applied to the grinding operation and checking the magnitude of working current being supplied to the workpiece after each such incremental change in said voltage, said changes being terminated and/or reversed when a predetermined relationship between voltage and current is attained.

(16) To provide apparatus, as aforesaid, in which sensing means is provided for successively and incrementally changing the voltage at which the working current is applied to the grinding operation and checking the magnitude of grinding current being supplied to the workpiece after each such incremental change in said voltage, said change being terminated and/ or reversed when the change in current magnitude resulting from a given voltage change falls Ibelow a predetermined minimum.

17) To provide apparatus, as aforesaid, which may by appropriate but relatively minor modifications of the basic equipment be arranged to respond to performance parameters other than the magnitude of working current, such as resistance across the gap between the grinding device and the workpiece or the rate of change in the rate of workpiece feed force or the spindle power.

(18) To provide apparatus, as aforesaid, in which the grinding condition is controlled as a result of a sensing of the workpiece feed force or by sensing of the applied spindle power.

(19) To provide apparatus, as aforesaid, which can be preset for fully automatic operation and will thereby maintain itself at the selected, including optimum, performance parameters without adjustment and without attention on the part of the operator expecting to insert and remove successive workpieces.

(20) To provide apparatus, as aforesaid, whchwill -be reliable and will, therefore, require relatively little maintenance to keep same in good operating condition.

(21) To provide apparatus, as aforesaid, which can be` readily applied with a minimum of modification to existing electrochemical grinding machines, such as the lmachine with only manual controls referred to in the above-mentioned U.S. patent to Bass et al., No. 2,922,258.

Other objects and purposes of the invention will be apparent to persons acquainted with apparatus of this general type upon reading the following disclosure and inspecting the accompanying drawings.

FIGS. |1-6 are graphs of observed and computed relationships between various control and performance parameters.

lIG. 7 is an illustration of a surface generated with variations in the voltage and feed force control parameters and the resulting variation in the current performance parameter. i

FIG. 7A is an enlarged fragment of FIG. 7.

FIG. 8 is a schematic side View of one typical electrochemical grinding apparatus wherein the working current is the selected performance parameter.

FIG. 9 is an enlarged showing of a portion of FIG. 8.

FIG. 10 is a schematic top view of the device of FIG. 8.

FIG. 1l is an enlarged showing of a portion of FIG. 1.

FIG. 12 is a schematic block diagram representing the system for controlling the selected control parameters of the electrochemical grinding apparatus.

FIG. 13A is a schematic electrical diagram of the system shown in FIG. 12.

IFIG. 13B is a schematic diagram of certain components of the apparatus shown in FIG. 8 and illustrating the electrical connection of the control thereto.

FIG. 14 is a chart illustrating the various functions which occur at predetermined time intervals.

iFIG. 15 is a side view of a grinding apparatus similar to that illustrated in FIG. 8 utilizing the spindle power as the selected performance parameter.

FIG. 16 is a side view of a modiiied grinding apparatus wherein the table feed rate is the selected performance parameter.

SUMMARY OF THE INVENTION The invention contemplates incrementally advancing a control parameter, such as applied voltage, from a selected starting point toward a selected, usually the expected optimum, operating range and after each such advance is effected the performance parameter (such as magnitude of working current) is measured and a record thereof is suitably stored. At a measurable point in time thereafter, the performance parameter is measured again and compared to said record. If the performance parameter change in relationship to the control parameter is, for example at a magnitude above a predetermined minimum value, indicating that the system is operating somewhere to the left of line A in FIG. 1, the control parameter continues to be incrementally advanced and is subsequently again sampled and the new sample similarly compared with the record of a previous sample, When, however, a given increment of control parameter advance results in a performance parameter change falling below said preselected minimum (such as when the system is between lines A and C of FIG. 11) the apparatus then automatically holds or reverses said control parameter at such values, by suitable subsequent sampling and adjusting, either to maintain said performance parameter within the selected range or to bring about whatever further adjustment is needed to follow such selected range if same should change during a grinding operation. This provides the continual searching action above referred to as one of the objects of the invention. While in the specific embodiment, hereinafter described to illustrate the invention, the selected parameters are the applied voltage and the feed force, and the selected performance parameter to be observed is magnitude of working current, other control parameters may be utilized as desired and as further described hereinafter to automatically search for, establish and maintain one or more selected performance parameters in an electrochemical grinding operation.

DETAILED DESCRIPTION In dealing with this problem a large amount of investigative work has been carried out to determine at a constant feed force the relationship between incrementally increasing voltage applied across the working zone (or gap) and the working current resulting therefrom passing through the working zone; between incrementally increasing voltage applied across the working zone and the gap resistance existing in the working zone at each voltage condition; between incrementally increasing the feed force applied to the working zone and the gap resistance existing in the working zone at each feed force; between incrementally increasing Working current passing through the working zone and power applied to a rotating abrasive electrode at each such current condition; between incrementally increasing current passing through the working zone and stock removal rate resulting from each such current condition and other and further similar and related relationships. As a result, a number of relationships have been established between the above-mentioned and other control parameters and performance parameters of the apparatus and some of such relationships have been discovered to be of such a nature that certain performance parameters, or changes therein, can -be taken as indicative of other conditions within the electrochemical operation and said conditions may thus be utilized to control the necessary control parameters to maintain said performance parameters at a desired value, usually an optimum value, both intrinsically and as related to each other.

As a specific example, attention is directed to FIGS. 1-6 wherein certain of the above-mentioned relationships are set forth for a work situation wherein tungsten carbide was the workpiece; the stock removal electrode was a rotating metal-bonded diamond impregnated grinding wheel; the electrolyte was a highly dissociatable material of the nature of alkali metal nitrate salts (meaning that in some cases the electrolyte contained a large proportion of such nitrates and in other cases other materials but in each case the electrolyte had a dissociation constant of generally the same order as alkali metal nitrates).

Under these conditions, it Will be observed by reference to FIG. l that with increasing voltage, the working current increases at a reasonably straight-line rate until it peaks at approximately seven volts at a table feed force of 31 pounds, then drops briefly, though sharply, before again resuming its rise. By comparing this figure to FIG. 4, it is seen that the gap resistance across the work gap increases sharply at the approximately seven volt point. While it is not fully known why this change in resistance occurs, it has been definitely observed and carefully measured and it is believed that a substantial quantity quantity of gas bubbles appear between the workpiece and the grinding Wheel at this point which displaces the electrolyte therefrom and thereby increases said resistance. However, the invention does not depend upon the correctness of this belief and same is stated only by way of possible explanation and not with any sense of reliance thereon or limitation. =Reference to FIG. 2 shows that at this same approximately seven volt point, the feed rate (stock removal) is at a maximum and then falls off drastically at higher voltages though only momentarily before resuming its upward trend. This falling off at higher voltages is believed related to the corresponding drop in Working current at higher voltages through the Work Zone inasmuch as the stock removal rate is by Faradays law proportional to the current passing therethrough. Lastly it will be observed from FIG. 3, that the spindle power is lowest at this same critical point, namely, approximately seven volts of applied potential across the working zone, and increases on either side of the low point which indicates that there is a maximum of electrochemical stock removal at this point and that stock removal at higher voltages is increasingly the result of mechanical grinding.

It will of course be accepted that the normal preferred relationship between electrochemical and mechanical grinding is when the electrochemical grinding operation has been maximized without causing the occurrence of any appreciable mechanical grinding. This optimum condition may be otherwise stated as that which results in a maximum stock removal rate with a minimum of mechanical grinding. T'he means for example, that for grinding tungsten carbide at a thirty-one pound feed force, the current passing through the working zone should be maintained at the peak corresponding to approximately seven volts, namely, for normal working purposes, between about A and B on the graph of FIGS.

1 and 11. Of course, it will be recognized that under some circumstances it maybe desirable to work in other areas of this curve.

'Referring now to FIG. 7, it is seen that a still more complex relationship is involved. Here the data presented in FIG. 1 is rearranged to show that a surface M is formed by variations in both feed force andvoltage and by the variations in current resulting therefrom. Thus, variations in either feed force or voltage will cause variations in current and simultaneous variations in both feed force and voltage will cause relatively complex variations in current. y.For illustrative purposes, it will be assumed that the desired operating condition is represented by the range R on the ridge E of the surface M. A further and detailed discussion of these operating data and the conclusions as to operating relationships to be derived therefrom appears in the laforementioned applicants paper. Although the shape characteristics of the surface 'M are substantially constant with time, the location of the ridge E, for example within the voltage feed force domain, can change very rapidly `witlitime due to changes in the area being ground and due further to changes vin the condition of the `face of the grinding device. Thus, under most factory operating conditions, it is entirely impracticable to expect operating personnel to maintain optimum performance parameters manually with the help only of voltage and current instruments and accordingly certain methods and specific apparatus for practicing said methods have been developed in order to put to practical use under normal factory operating conditions the data. discussed above.

Whilethe control concept and method so developed represents the more fundamental aspect of thepresent invention, it is more readily understood in connection with apparatus for practicing said method and, accordingly, attention will now be toward such apparatus and the method will become apparent as the description of such apparatus progresses...v

Referring now to FIG. 8, there is schematically illustrated a conventional electrochemical grinding apparatus 10, hereinafter referred to as ECG apparatus, essentially as set forth in the U.S. patent to Keeleric, No. 2,826,540. Insaid device, a grinding device 11, here an abrasive wheel (such as one utilizing diamond or other grit of relatively low electrical conductivity bonded with metal), is mounted on a rotatable spindle or shaft 12, which shaft is driven by a spindle motor 13 supplied with electrical power from power lines L1, L2 and L3. A workpiece vW is supported by a `suitable fixture 14 which in turn may bemounted on a reciprocable table 16. In the particular machine schematically illustrated in FIG. 8, the table 16 is mounted on suitable means such as rollers, one of which.

is-indicated at 18, onto a frame 17 which is further supported in any convenient manner. Electrical insulation is providedrsomewhere between the workpiece W and the frame, such as the insulation 15 shown between the lixture 14 and the table 16. A workpiece feed force may be applied to the table 16 for automatically causing the workpiece W to bear against the abrasive grain of the grinding device with a controllable pressure. In this particular embodiment, the feed force is applied by an air cylinder device 21 which is controlled by a valve 22. An air pressure sounce 23 is connected to an electropneumatic transducer 25 which controls the pressure of air supplied to the valve 22. The valve 22 then commands the direction of movement of the piston 24 in the air cylinder device 21 and the table 16 connected thereto at a force determined by the degree of energization of the electropneumatic transducer 25. The electropneumatic transducer 25 may be of any well known variety such as a Moore Model 77 transducer made by Moore Products Company of Spring House, Pa. In the particular illustrated embodiment, the transducer 25 is preset to allow a pressure of 3 p.s.i. to pass therethrough, even when unenergized, to the valve 22 the distance the table 16 can move toward the grinding device 11 in response to the feed force. The limit switch 19 is here responsive to an engagement with the end of the table 16 and is usually adjusted for actuation before, but only slightly before, the table encounters the positive stop 20.

A nozzle 26 supplies electrolyte to the grinding zone as further described in the above-mentioned Keeleric patent. The positive side of a source S of low voltage D.C. potential is connected either directly to the workpiece W or it may be applied asv convenient to the workpiece W through the fixture 14, as shown. The negative side of the source S is connected to the shaft or spindle 12 on which the grinding device 11 is mounted by means which, for example, may be the same as that disclosed in U.S. patent to Robischung et al., No. 3,115,454. The source S may be of any convenient source of essentially ripple-free D.C. potential, which may be supplied by storage batteries but, in the practical case, is more usually supplied by an adequately rectified commercial line potential.

The foregoing except for the electropneumatic transducer 25, refers to a typical ECG apparatus utilizing a metal-bonded grinding wheel as the grinding device. It is recognized, of course, that other types of grinding devices already known in ECG processes, may be used with the above-discussed ECG apparatus, such as the abrasive belt means shown in U.S. patent to Bell, No. 3,162,588 or the abrasive disk means shown in U.S. application to Bell, Ser. No. 572,030, filed Aug. l2, l966,n0w abandoned, and assigned to the same assignee as the present invention and further detailed in U.S. Pat. No. 3,334,041.

The vECG apparatus described hereinabove forms no part of the present invention and is described solely for convenience in reference. The invention resides in the method and apparatus concepts embodied in the control device, 27 which automatically controls both the voltage applied to the workpiece W by the source S and the table feed force by the electropneumatic transducer 25 to maintain the working current within the range R on the surface M (FIG. 7).

In the first embodiment of the invention, the control apparatus 27 is responsive to the working current flowing through the conductor 28. This could alsoy be said to be responsive to the resistance across the gap between the workpiece W and the grinding device 11 since the measurement `of resistance is actually accomplished bythe measurement of current. In this particular system, however, the working current is detected by a shunting device 29 which supplies a signal through the conductor 31 to the control apparatsu 27. The control apparatus 27 also provides a signal through conductor 32 to the electropneumatic transducer 25 for regulating changes in the table feed force above a preselected initial value, such as the force vprovided by a feed pressure of 3 p.s.i., upon the appearance of a Working current through the workpiece W.` The control apparatus 27 is also responsive to signals received from the limit switch 19 through the conductor 33 to control the valve 22 through a pair of conductors 34 and 35 to reverse the pressure applied to the cylinder 21 whereby to initiate a retraction thereof.

Turning now to the details of the control apparatus 27 and discussing for the present the method aspects of the invention in terms of one preferred apparatus for practicing same, the control apparatus 27 comprises three sections as illustrated in FIG. 12, namely, a timing section 36, an analytical section 37 and a logic section 38. The

timing section 36 is responsive to timing` pulses of a predetermined timed interval to control the functions to be performed by the analytical section 37 and the logic section 38. In this particular embodiment, the timing pulses kare generated from a magnetic sensor 39 (FIG. 8) which is positioned in close association with the hub 41 of the grinding device 11. The hub 41 may be provided with a plurality of magnetic pole pieces (not shown), for example, which, as the hub 41 rotates, are detected by the magnetic sensor 39 which in turn supplies a signal through the conductor 42 to the timing section 36. The number of pulses per revolution can be any number so long as the analytical section 37 and the logic section 38 will vbe responsive to the signals generated by the timing section 36. In this particular embodiment, four pulses per revolution are generated and fed through the conductor 42 to the timing section 36.

A synchronized pulse train is generated at the output terminals 43, 44 and 4S of the timing section 36 and is applied through conductors 46, 47 and 48 to the analytical section 37 and through conductors 49, 50 and 51 to the logic section 38.

The analytical section 37 is responsive to the signal generated in the shunting device 29 and supplied thereto through the conductor 31. This signal represents an analog of the work current actually flowing through the workpiece W. The analytical section 37 analyzes the signal received from the shunting device 29 and determines whether the voltage generated by the source S and the table feed force controlled by the transducer 25 should be increased or decreased. Once that determination has been made, a signal is generated and sent through the conductor 52 to the logic section 38. The analytical section 37 also provides a signal through the conductor 32 to the electropneumatic transducer 25 (FIG. 8) for causing an appropriate supplement to the initial air pressure supplied to the cylinder 21 to cause the workpiece W to bear against the grinding device with a determinable pressure upon the appearance of a working current through the workpiece W. The circuitry for starting the apparatus will be discussed in more detail hereinbelow in connection with the circuitry illustrated in FIGS. 13A and 13B.

The logic section 38 is responsive both to the synchronized pulse train from the timing section 36 and to the signal from the analytical section 37 which informs the logic section whether the voltage applied to the workpiece should be increased or decreased. The decision of the logic section is then sent through conductors 53 and 54 to the source S for either increasing or decreasing the voltage applied to the workpiece. A feedback signal is generated in the logic section 38 and sent through conductor 55 back to the analytical section 37 so that the analytical section is aware Iat all times of the condition of the source S. The logic section 38 is further responsive to the signal received from the limit switch 19 through the conductor 33, which response is sent through the conductors 34 and 35 to the 'valve 22 for reversing the air pressure in the cylinder 21 and initiating the retraction of the table 16.

FIG. 13A illustrates one embodiment of the timing section 36, analytical section 37 and logic section 38 and FIG. 13B illustrates conventional starting and operating mechanism as modified to utilize the present invention. It is recognized that other circuits may accomplish the same result and, therefore, the following description is not intended to be limiting but is instead set forth solely to illustrate the invention. The various gating circuitry is well known and only the symbol for the type of gate has been illustrated for convenience in reference. The gating nmenclature is illustrated and the characteristics are described in a publication by John L. Hughes, entitled Computer Lab Workbook (l968'ed.) published by Digital Equipment Corporation of Maynard, Mass.

The timing section 36 is supplied with spiked pulses from the sensor 39 through the conductor 42 and through a sensor converter 56 which converts the spiked pulses to square-wave pulses in order to obtain a more accurate and precise operation of the timing section 36. A conductor 57 connects the sensor converter 56 to a counter 58 of any conventional type having a power input terminal 59 connected to any independent source 61. In this particular embodiment, three outputs are generated at the output terminals 43, 44 and 45, and supplied to the conductors 46, 47 and 48, respectively, and conductors 49, 50 and 51, respectively. The output conductors 43, 44 and 45 of the timing section 36 are energized according to the table illustrated in FIG. 14, the shaded bars indicating the on condition of the respective outputs.

Conductors 46, 47 and 48 are connected, respectively, to the inputs of the AND gates 1 and 2, conductor 46 however, being connected to gate 2 through an inverter 69. Conductor 48 is further connected to the winding 62 of a normally open relay 63 to oppose the power source 64. The output 71 of the AND gate 1 is connected through the winding 72 of a normally closed relay 73 to oppose a power source 74. The output 76 of the AND gate 2 is connected to input 1 of the up-down memory circuit 77. The up-down memory circuit 77 may be of any conventional type such as a Data lip-op (one-half of a Digital Equipment Corporation K202) which has the characteristic of transferring the signal at input 2 to the output 122 when input 1 is enabled. That is, if input 2 is HI when input 1 is enabled, the output 122 will also be HI. If input 2 is LO when input 1 is enabled, the output 122 will also be LO.

The conductor 31 connects the shunting device- 29 to a pair of conductors 78 and 79 for supplying an analogue of the working current actually appearing in the working circuit to the analytical section 37. The conductor 78 is connected to one terminal 81 of the relay 63, the other terminal 82 being connected through a variable Calibrating resistance GC-1 to the input 83 of amplifier A, which may be of any conventional type. The input 83 is also connected to the terminal 84 of the relay 73. The other terminal 86 is connected to the output 87 of ampliiier A. A capacitor 88, whose function will be described hereinafter, is connected betwee the input terminal 83 and the output terminal 87 of amplifier A. The output terminal 87 of amplifier A is connected to two conductors 89 and 91. Conductor 89 is connected to the input 92 of amplier D. Conductor 91 is connected to the input of ampliiier C.

Conductor 79 is connected through a gain control resistor 94 to an input terminal 96 of amplifier B. The output terminal 97 of amplifier B is connected to three conductors 101, 102 and 103. Conductor 101 is connected to the input 104 of the sensor converter 106 and to conductor 32. The

conductor 32 is connected to the electro-pneumatic transducer 25 illustrated in FIG. 13B. Conductor 102 is connected to the input 107 of ampliiier C. Conductor 103 is connected to the input 108 of amplifier D.

In this particular embodiment, amplifiers C and D are very high gain dilerential ampliers of the type which saturate very quickly when the potentials are according to the signs on the input terminals to produce an essentially on-oii output in response to a variable input.

The output 111 of ampliier C is connected to an input of AND gate 3. The output 112 of amplifier D is connected to an input of AND gate 4. The output 113 of AND gate 3 is connected to an input of an OR gate 5. The output 114 of AND gate 4 is connected to another input of OR gate 5.

The output 116 of the sensor converter 106 is connected through a conductor 117 to one input of the NAND gate 6. The other input of the NAND gate 6 is pre-enabled through the connection to a potential source 118. The output 119 of the NAND gate 6 is connected to the remaining input of OR gate S.

The output 121 of OR gate 5 is connected to input 2 of the up-down memory circuit 77. The output 122 of the up-down memory circuit 77 is connected through conductor 52 to an input of AND gate 7 in the logic circuit.

Turning now to the logic section 38, the limit switch 19 (FIG. 8) supplies a signal through the conductor 33 to a converter 123 which converts an A.C. signal into a digital signal. The output 124 of the converter 123 is connected to two conductors 126 and 127. The conductor 126 is connected through an inverter 128 to the remaining input to the AND gate 7. The output 129 of the AND gate 7 is connected to three conductors 131, 55, (including 55A and 55B), and 132. The conductors 55 and 55B are connected to the remaining input to AND gate 3. The conductors 55 ,and 55A are connected throughan inverter 136to the remaining input to AND gate 4.

The conductor 127 is connected to the input to an adjustabletime delay 137. The output 138 of the adjustable time delay 137 is connected to two conductors 141 and 142. The yconductor 141 is connected to the winding 143 of a normally open relay 144 to oppose a potential source 146. The terminals 147 and 148" of the relay `144 are connected through a pair of conductors generally referred by 149 and 150 to supply a signal to the solenoid of the valve 22 in the section 225 (FIG. 13B) described hereinbelow to reverse the pressure in the cylinder to cause a retraction of the table 16.

The conductor 142 is connected to an input to NAND gate 8. The other input of the NAND gate 8 is pre-enabled through a connection to a potential source 151. The output 154 of NAND gate 8 is connected to the reset terminal 156 `on the counter 153. A LO signal at terminal 156 will reset the counter to zero and a HI signal will maintain the counter in its then existing condition. The output 129 of AND gate 7 is connected through conductor 131 tothe up-down controlling terminal 152 on a counter 153. More` particularly, the up-down controlling terminal .will accept either a HI or a LO signal which will cause the counter to either count up or count down. For example, a HI signal applied to the terminal '152 will result in an up count in the counter 153 during the rise of a pulse appearing at the input terminal 167. Similarly, a LO signal `applied to the terminal 152 will result in a down count in the counter 153 during the fall, or at `the trailing edge of a pulse appearing at the input terminal 167. The power terminal 157 of thhe counter 153 s connected to a source of potential 158.

The counter 153 functions in the same manner as the counter 58 in the timing section 36. That is, the various levels 1, 2, 4 and 8 will be turned on and olf in predetermined patterns and in a conventional manner upon the arrival of successive pulses at counting terminal 167. The counter section having the levels and 20 will be connected `in a conventional manner to count every pulse number 10 and 20, respectively.

The output 116 of the sensor converter 106 is also connected through a conductor 161 to an input to AND gate 9. Conductors 49 and 50 from the timing section 36 are connected through inverters 162 and 163, respectively, to two inputs to the AND gate 9 and conductor 51 is connected to the remaining input. The output 164 of AND gate 9 is connected to one input to AND gate 10. The output 166 of AND gate 10 is connected to the counting terminal 167 of the counter 153. Whenever a pulse is received at the counting terminal 167, the counter 153 will be either counted up or counted down, depending on whether a HI or LO signal is present at the terminal '152.

The counter 153 is provided with a plurality of output terminals 17.1"-176 Each of the output terminals 171-176 except 172 and 173 is connected to the inputs to AND gate 11. Furthermore, each of the outputs 171-176 is connected through inverters to the inputs to AND gate 12. The remaining input'to AND gate 11 is connected to conductor 132 and the output 129 of AND gate 7. Conductor 132 is also connected through an inverter to the remaining input to AND gate 12. The outputs 177 and 1F78 of AND gates 1.1 and 12, respectively, are connected to the inputs toNOR gate |13. The output 179 of NOR gate 13 is connected to the remaining input to AND gate 10.

When the counter 1'53 is at a minimum count or zero and the counter 153 is instructed to count down as indicated by a LO on conductors 152 and 132, all of the vconductors 152 and 132, all of the inputs to AND gate 11 are HI and enabled to give a HI signal at the output 177. This output is transferred to a LO through NOR gate 13 to disenable one input to AND gate 10. Thus, again,

In o further counting pulses can be sent to the terminal The output terminals 171-176 of the` counter 153 are connected to the windings 181-186, respectively, of normally open relays 191-1196 to oppose a common source of potential 197 respectively through each of said windings. Thus, a HI value on a given grouping of outputs of the counter 153 will oppose such common potential as same.

appears on the corresponding relays permit same to open. The terminals of each of the normally open relays 19,1- 196 are connected to shunt, when closed, a plurality of series-connected resistors 201-206, respectively. The resistors 201-206 are connected in any conventional manner to a control connection of a conventional DtC. generator S having output connections 211 and 212 and energized from a source 208. The internal connections of the D.C. generator S are of a coventional type and in this instance arranged so that an increasing resistance in the serial group 201-206 will provide an increasing potential across the output terminals 211 and 212. Thus, when the relays 191-196 are open, the resistors 201-206 are all in circuit and the voltage output of the generator S is at its maximum andas each resistor is, or selected groups of resistors are, shunted out of the circuit the voltage output of said generator is decreased by controllable increments. The resistor 209 in the conductor 53- is to insure that a finite starting voltage will be produced by the generator S when the apparatus 10 yis initially energized.

The starting section 22'5 (FIG. 13B) is supplied by electrical energy from two of the three power lines L1, L2 and L3 which supply electrical power 'to the spindle motor :13. More particularly, the primary winding 2% of the transformer 227 is connected to the lines L2 and L3. The secondary winding 228 is grounded on one side at 22l9' on one side. The ungrounded side of the secondary winding 228 is connected through a fuse and master stop switch 231 to a conductor 232. The grounded side of the secondary winding 228 is connected to a conductor 233.

A series connected pair of switches 23-4 and 236 and a relay winding CRI are connected between the conductors 2%32 and 233'. The switch 234 is normally closed and the switch 236 is normally open. The normally open contacts CRI-1 of the relay `CRI are connected across the switch 236. -The normally open contacts CRi1-2, CRI-3 and CRI-4 are connected in series with the power lines L1, L2 and L3, respectively supplying the spindle motor 13. The normally open contacts CRI-5 are series connected with a relay winding CRZ between the conductors 232 and 233.

The conductor (FIGS. 13A and 13B) is connected to the conductor 232. The conductor 149 is connected to one side of a normally open switch 237. The other side of the switch 237 is connected through a normally closed switch 238 and relay winding CR3 to the conductor 233. v

`the source 208 and the generator S (FIG. 13A).

13 OPERATION The operation of the device embodying the invention will be described in detail hereinbelow for a better understanding of the invention.

The operation of the basic ECG apparatus, namely the grinding device 11, the workpiece W and the potential applying circuitry including the source S, all proceed as already well known and particularly as set forth in the above-mentioned patent to Keeleric.

More particularly, however, the start switch 236 (FIG. 13B), is closed to energize the relay winding CR1 to close the contacts CR1-2, CR1-3 and CR1-4 and energize the spindle motor 13 to start the grinding device rotating. Contacts CRil-l close to lock in the relay CR1 so that pressure holding the start switch 236 closed can be removed. Contacts CR1-5 close to energize the relay CR2 to close the contacts CR2-1 and CR2-2 between the source 208 and the generator S (FIG. 13A).

The solenoid 239 on the valve 22 and the transducer as yet are unenergized so that the transducer 25 at this point supplies only a force corresponding to a 3 p.s.i. feeding pressure to the cylinder 21 to retract the piston 24 and worktable 16. The apparatus is now in a condition for the operator to load a workpiece W into the fixture 14. After the fixture has been loaded, the operator then closes the manual switch 237. Since the limit switch 19 is not as yet supplying a signal on the conductor 33, the relay 144 (FIG. 13A) is energized by the source 146 to close the contacts between the terminals 147 and 148 and conductors 149 and 150. Thus, a closing of the switch 237 will energize relay CR3 to close the contacts CF3-1 to lock in the relay CR3 and close contacts CR3-2 to energize the solenoid 239. This causes the valve 22 to reverse the supply of air to the cylinder 21 and to cause the workpiece W to advance toward the grinding device 11. However, since the transducer is as yet still unenergized, the table 16 will advance with only the force developed by the minimum air pressure, here 3 p.s.i.

The apparatus is accordingly started and the workpiece is about to contact the grinding device. When it does so, working current will oW and the process and apparatus of the invention will be started.

In applying thereto the concept of the present invention, the magnetic sensing device 39 (FIG. 8) will pick up pulses from the magnetic pole pieces (not shown) connected to the hub 41 of the grinding device 11 when the grinding device 11 is rotating and will supply a series of pulses spaced apart a predetermined time interval to the control apparatus 27. In this particular embodiment, the timing pulses are transmitted to the timing section 36 through the conductor 42 so that a synchronized pulse train is produced in varying patterns on each of the output terminals 43, 44 and 45 of the timing section 36. FIG. 14 illustrates the intervals during which the output terminals 43, 44 and 45 are respectively turned on and of. For example, the conductor 43 is turned ott during time interval I, turned on during interval II, turned off during interval III and continuing alternately on and oii through the remaining time intervals illustrated in FIG. 14. Output terminal 44 is turned off for two time intervals I and II and then turned on for two time intervals III and IV and then turned off again for two time intervals V-VI and so on. Output terminal 45 is turned off for four time intervals I-IV and then turned on for four time intervals V-VIII and is then turned off for four time intervals I-V during the next cycle of eight time intervals. Thus, for all time intervals I, all of the terminals 43, 44 and 45 are turned oi. At all time intervals VIII, all of the output terminals 43, 44 and 45 are turned on.

The foregoing described synchronized pulse train is applied to the inputs of the AND gates 1 and 2.

A comparison of FIG. 14 with the inputs 46, 47 and 48 to the AND gates 1 and 2 will indicate that AND gate 1 will remain in an olf condition through pulse intervals I-VII and will be turned on only during time interval 14 VIII, AND gate 2 will be turned on only during time intervals VII.

In starting the machine, the control 27 is energized and the wheel is rotating but for the moment assume that the operator has not closed the start switch 237. Thus, the workpiece W is not engaging the grinding device 11 and, as a result, no working current will iiow. Under such conditions there is no current on conductors 31, 78 and 79 so that capacitor 88 cannot be charged and there is no input to ampliers A and B. Thus, there will be no out puts at the output terminals 87 and 97 of amplifiers A and B, respectively, and likewise no output at terminals 111 and 112 of ampliers C and D, respectively. This provides a LO signal on the conductor 117 connected to one input of NAND gate 6. However, there will be a HI output at the output terminal 119 of NAND gate 6 due to the fact that both inputs have not been enabled. The HI output signal is supplied to an input of OR gate 5 which will then be applied as a HI signal to input 2 of the updown memory circuit 77. AND gate 9 will not yet be turned on at time interval V (as willhereinafter appear as the normal operationg function) because there is no working current supplied to the workpiece and no analog supplied through amplifier B to conductor 161. The HI signal at input 2 of the up-down memory circuit 77 will remain until time interval VII wherein AND gate 2 is turned on so that the HI output at terminal 76 will be fed to input 1 of the up-down memory circuit 77 to cause the HI signal at input 2 to be transferred to the output terminal 122. The signal at the output terminal 122 will be conducted through conductor 52 to an input of AND gate 7. Since the end of the table 16 is spaced away from the limit switch 19, there will be no signal supplied to the converter 123 and in turn no signal supplied to the conductors 126 and 127. Thus, there is no current through the time delay circuit 137 and none on the winding 143 to oppose the source 146. Hence, the relay 144 Will be energized to close the contacts between terminals 147 and 148. However, the inverter 128 will result in an input to AND gate 7 and since both inputs will then be enabled, a HI signal will exist at the terminal 129 which will be fed through the conductor 131 to the up-down terminal 152 of of the counter 153, -whereby NAND gate 6 assures that the counter 153 will be set to count up to increase the voltage as soon as a working current is present regardless of the condition thereof at its last previous operation.

At the beginning of-time interval I, the signal on conductor 48 will be LO whereby there is no potential to oppose the potential source 64 and same will energize the winding 62 of the normally open relay 63 to cause the terminals 81 and 82 to close. At this time, AND gate 1 will be turned olf so that the potential at the output 71 will be LO to thereby permit the potential source 74 to energize the winding 72 of the normally closed relay 73 to open the normally closed connection between the terminals 84 and 86. Thus, when the switch 237 is closed to advance the workpiece W toward the .grinding device 11, when the workpiece W contacts the grinding device 11, current will iiow from the shunting device 29 through the conductors 31 and 78 and will charge the capacitor 88. This is represented in FIG. 14, with the charge on the capacitor 88 reaching the value T during time interval III. It is recognized, of course that the rate at which the capacitor 8-8 becomes charged during the interval is regulatable by the variable resistor GC-l.

Further, the appearance of a varying working current will place a varying HI signal on conductor 101 which is converted to stable HI signal applied to the conductor 117 by the converter 106 and thereby places a LO value on conductor 119. This removes its iniluence from OR gate 5 and thereafter leaves the voltage at input 2 of the updown memory 77 to be governed by the outputs of AND gates 3 and 4 as hereinafter described.

At time interval IV, nothing will change but at time interval V, outputs 43 and 44 are LO and output 45 is HI.

This produces no change in the AND .gates 1 and 2 but, since as above noted, conductor 161 is now HI, this pattern of output through conductors 49', 50' and 51 from the counter 36 enables the AND gate 9 and this produces a Hl output on conductor 164 and enables one input of AND gate 10. Assuming at this point that the voltage output of the generator S is near, and perhaps even at, the bottom of that part of the voltage controlled by the updown counter 153, this means that there will be no output from either of the. AND gates 11 and 12 and hence a HI level on conductor 179. This enables the other input of AND gate 10 to produce a HI pulse on conductor 166 and thereby to supply `a pulse to the terminal 167 of the counter 153. Since the system has been set to advance the voltage, there will already be a HI signal at the output129 ofl AND gate 7 and at the terminal 152 on the counter 153. Therefore, a pulse appearing at the terminal 167 will, in this embodiment, advance the counter by one binary count which will result in an opening or closing of appropriate ones of the relay switches, and the connection or shunting or corresponding ones of the resistances 201-206 with respect tothe lcircuit of the generator S, whereby to effect an incremental increase in the voltage. The incremental increase in voltage has been represented in FIGS. 1l and 14 as the new value U.

Simultaneously with the foregoing, at the beginning of time interval V, conductor 48 will be HI so that the voltage applied to relay I63 from source 64 will be opposed and relay 63 will thereby become de-energized and the terminals 81 and `82 will open. Thus, the charging of the capacitor 88 is terminated and the potential thereon is stored.

The new value of voltage U above mentioned will result in an increase in the instantaneous current detected by the shunting device 29, which will, in turn, supply a new signal through the conductors 31 and 79 to amplifier B which vwill then supply a signal to the inputs 107 and 108 ofv amplifiers C and D, respectively. If the instantaneous voltage value U is higher than the stored value T on the capacitor 88, amplifier C will saturate and produce an on output so that a HI signal is supplied to an input of AND gate 3. Since a HI signal` already exists on the output 129 of AND gate 7, the remaining input to AND gate 3- will be enabled by the HI signal being sent thereto through the conductorsSS and 55B so that a HI signal will appear atthe output 113 and at an input to OR gate 5. This HI signal will then be transferred to the output 121 of OR gate 5 and supplied to input 2 of the up-down memory circuit 77. Nothing further happens in the time interval, nor in time interval VI.

At time interval VII, conductor 43 is LO and conductors 44 and 45 are HI. This results in AND gate 2 being turned on so that a HI signal is supplied to input 1 of the up-down memory circuit 77. Atv this time, the signal at input 2 of circuit 77 will be transferred to the output 122 and sent through the conductor 52.to AND gate 7. Since both gates of the AND gate 7` are now enabled, a HI signal` will be present at the output 129, which HI signal will'be supplied to the terminal 152 on the counter 153. `This will signal the counter 153 to perform an up count upon the occurrence of the next counting pulse to the terminal 167.

At the beginning of time interval VIII, all of the inputs to AND gate 1 will be HI and enabled so that an output will appear at 71 twhich will then oppose the voltage applied from source 74 and thereby de-energize the relay 73 to close the normally closed contacts between terminals 84 and 86 to ydischarge the capacitor 88.

Simultaneous with the foregoing, the varying signal on the conductor 32 represents an analog of the working current and will varyingly energize the electro-pneumatic transducer 25. The transducer 25 will increase the pressure applied to the valve 22 and cylinder 21 with increasing magnitudes of current on the conductor 32. Likewise, the transducer will decrease the pressure applied to 16 the valve 22 and cylinder 21 with decreasing magnitudes of current on the conductor 32.

The value by which the transducer permits the pressure to increase relative to increase in working current is regulatable by the variable resistor GC-2. `More particularly, the amount of pressure increase or decrease can be set so that the values of voltage and working current searched for will be maintained on the surface M as illustrated in FIG. 7. However, for the purpose of presenting a clear understanding of the function performed by the control 27, yfurther discussion of the control of the feed force will be deferred until later after the discussion relating to the control of the voltage and the variations in the working current have been more fully developed and as hereinafter described.

yUpon the occurrence of the second `time interval I, relays 63 and 73 will perform in the same manner as discussed hereinabove with respect to the first occurrence of a time interval I. However, the capacitor 88 will now charge to the new voltage value U. At the beginning of the second time interval V, relay 63 will again be de-energizled and the contact between terminals 81 and 82 will again be opened. This will result in the capacitor 88 this time storing a voltage equal to the value represented by U and applying said potential to terminals 92 and 93 of amplifiers D and C, respectively.

Simultaneously therewith, at the beginning of the second time interval V, AND gates 9 and 10 will be turned on to supply a pulse to terminal 167 to advance the counter 153 one count. This will result in an incremental increase in voltage to a new value X. This new incremental increase in voltage will be detected by the shuntng device 29, which in turn will supply a signal through conductors 31 and 79 to amplifier B and to the inputs 107 and 108 of amplifiers C and D, respectively. In this particular eX- ample, it will be assumed that the difference between voltage value U and voltage value X is now below a predetermined minimum. In such case, the potential differential is not great enough to turn either amplifier C or D on and they remain in the off condition so that no signal is applied to the AND gates 3 and 4 and OR gate 5. When no signal is appliedto the aforementioned gates, there will be a LO output at 121 of or gate 5, which LO signal will be supplied to input 2 of the up-down memory circuit At the second time interval VII, AND gate 2 will again be turned on to result in a transfer of the LO signal at input 2 to the output 122, which LO signal is supplied through the conductor 52 to the input to AND gate 7. This LO signal will not enable the input to gate 7 so that a LO output will appear at 129, which LO signal is supplied through conductor 131 to the controlling terminal 152 of the counter 153. This will signal the counter to count down one count upon the appearance of the trailu ingl edge of the next counting pulse at terminal 167.

At the beginning of the second time interval VIII, all of the inputs to AND gate 1 will be HI and enabled so that an output will appear at 71 to de-energize the relay 73 resulting again in a closing of the normally closed contacts to connect the terminals 84 and 86 and again to discharge capacitor 88.

At the third time interval I, relay 63 will close to connect the terminals 81 and 82 together and the relay 73 will be opened to disconnect the terminals 84 and 86. Thus, the capacitor 88 will be charged through the conductors 31 and 78 to the voltage value X.

At the beginning of the third time interval V, relay 63 is de-energized to discontinue the charging of capacitor 88. Thus, the voltage value X will be stored on the capacitor 88 and supplied to the linputs 92 and 93 of amplifiers D and C, respectively. Simultaneously therewith, the inputs to AND gates 9 and 10 are enabled so that a counting pulse will appear at the terminal 167 of the counter 153. Since the signal at terminal 152 is LO, the counter will count down to thereby decrease the volt- 17 age by an incremental value. This value has been represented by Yin FIG. 14.

The incremental decrease in voltage is detected by the shunting device 29 and a signal is supplied through conductors 31 and 79 to amplifier B and the inputs 107 and 108 to amplifiers C and D. Since, in this particular example, the instantaneous voltage value Y is less than the stored value X on capacitor 88, but said difference being greater in value than said predetermined minimum, amplifier D will saturate and be turned on so that a HI output is generated at 112 and is supplied to an input of AND gate 4. Furthermore, since the output at 129 of AND gate 7 is LO, a LO signal is supplied through conductors 55 and 55A to the inverter 136, which inverts the signal to a HI signal to enable the remaining input to AND gate 4 to generate a HI signal at the output 114. This HI output is then supplied to an input to OR gate 5, which HI signal is then transferred to the output 121 and thence to input 2 of the up-down memory circuit 77.

At the third time interval VII, all of the inputs to AND gate 2 are enabled so that a HI signal will appear at input 1 of the up-down memory circuit. This will result in a transference of the HI signal at input 2 to the output 122, which HI signal is delivered through conductor 52 to enable the remaining gate of AND gate 7 to generate a HI signal at the output 129 and to the up-down terminal 152 of the counter 153 to eifect an up count when the next counting pulse arrives at terminal 167.

At the third time interval VIII, all of the inputs to AND gate 1 are H'I and enabled resulting in an output at 71 which de-energizes relay 73 to close the contacts between terminals 84 and 86 to discharge capacitor 88.

Thus, it will be recognized that for so long as incremental increases in voltage applied to the working circuit result in an increase in current therethrough of more than a predetermined amount, the counter 153 will continue to call for continued increase in the voltage and the system will follow the upwardly sloping portion of the curve shown in FIGS. 1 and 11. However, when the voltage increase results in less current increase than such predetermined minimum, it indicates that the system is approaching the peak of the current-voltage curve of FIG. 1 and is accordingly approaching the predetermined, here optimum, operating condition desired. However, since it is not desired for the system to move past the peak of said current-voltage curve, the voltage is reduced and the system caused to move back (leftwardly and downwardly) along said current-voltage curve. If the resulting drop in current remains below said predetermined minimum (said minimum being a numerical value having no relation to whether the dilference is an increase or a decrease in working current), the signal on the counter 153 will continue to indicate a down count and the voltage will be reduced again. However, when the amount of current difference again exceeds the predetermined minimum so that the operation is back into the steeper portion of the current voltage curve (as near step A in FIG. 11), then the signal on the counter 153 will again reverse and call for an up count. In this manner, the cycles will repeat in the manner above described and the voltage and resulting current will cycle back and forth in a region between A and B of said current-voltage curve as appearing in FIGS. 1 and 11. Thus, the operation as described will maintain the applied voltage at the desired value and maintain the working current at its maximum even when the sluggish response of the generator to initial voltage increases causes an overshooting of the crest of the current-voltage curve of FIG. 1. The logic decision to decrease voltage even though it does not appear until region B-C of FI'G. 11 has beenvreached will continue until points B or A are reached and finally will stabilize at about point A as previously described.

The apparatus will work acceptably for certain purposes as above described if the table feed force is maintained at a constant value. However, the apparatus will work t 18 the full intent of the invention if the table feed force is also made variable. That is, and referring now to the preferred embodiment embodying a control of the feed force with reference being had to FIGS. 7, 11, 13A and 13B, the fluctuations in the working current will be detected by the shunting device 29 and fed to the B amplifier through the conductors 31 and 79. As the working current increases, a signal of increasing magnitude will be fed from the output of amplifier B by conductor 32 to the transducer 25 to increase the air pressure supplied to the valve 22 and cylinder 21 to urge the workpiece against the grinding device with an increasing force. Likewise, when the magnitude of the current diminishes, the magnitude of the pressure will decrease correspondingly to decrease the force urging the workpiece against the grinding device.

Thus, with reference to FIG. 7A, and assuming that the feed force pressure is already at 3l-l-A1 pounds, an increase in the magnitude of current to a value T will produce a feed force pressure of 31-l-A2 pounds. A further increase in the magnitude of current to a value U will produce a feed force pressure of 31|A3. This will cause the control 27 to search along the line L in FIG. 7A between the lines A and B. The three-dimensional movement of the operating point determined by the movement of control parameters of voltage and feed force will maintain the machine within the desired operating range R on the crest of the ridge 1E.

The foregoing-described operation will continue until the work table contacts the limit switch 19 indicating that the workpiece has been ground to the desired dimension. When the table 16 strikes the limit switch 19, an A.C. signal will be supplied through the conductor 33 to the converter 123, which signal will be converted into a digital signal and supplied to the inverter 128 of the AND gate 7. This will disenable the input to AND gate 7 and cause a LO signal to appear at the output 129, regardless of signals which may continue to appear on conductor 52, which LO signal will remain until the signal on conductor 33 is discontinued. This initiates a down counting operation regardless of the signals which continue to appear on conductor 52. The resultant drop in voltage and current will simultaneously reduce the table feed force. After a short time delay during which the grinding operation is nished off to improve the surface finish and surface flatness and any mechanical strain in the grinding machine relieved, the conductor -142 will supply a HI signal to NAND gate 8 so that both inputs are then enabled. This will result in a LO signal at output 154 and terminal 156 to reset the counter 153 to zero.

Further simultaneously therewith, the delayed signal at the output 138 will be supplied through the conductor 141 to oppose the source 146 resulting in a de-energization of the winding 143 of the relay 144. Since the relay 144 is in series with the table advancement circuitry consisting of the relay CR3, the table advancement will be discontinued upon breaking the circuit between the conductors 34 and 35 to de-energize the solenoid 239 of the valve 22 to reverse the air supplied to the cylinder 21 so that the table 16 and workpiece W are retracted from the grinding from the grinding device 11. Since the counter 153 has already been reset to zero, the current is low and the transducer will have reduced the air pressure supplied to the valve 22 to 3 p.s.i. Then, the table 16 will retract at a force corresponding to such 3 p.s.i. feeding pressure.

MODIFIED CONSTRUCTION The embodiment illustrated in FIG. 15 is essentially identical to the embodiment illustrated in FIG. 8. However, in this embodiment, the working current flowing t0 the workpiece W is not the parameter which is detected. Instead, a sensing device 216 for detecting the power drawn by the spindle motor 13 is placed in sensing relationship with the input lines L1, L2 and L3 to the motor. The control system 27A is constructed so that it will be sensitive to a condition of minimum power at a given operating feed force (lFIG. 3), which minimum power assuming a table feed force of 31 pounds, for example, occurs in the voltage range of approximately 6-7 volts for the grinding conditions above described with respect to which these data were collected. The signal produced by the, sensing device 216 is supplied through a conductor 217 to the control device 27A. The conductor 217 corresponds tothe conductor 31 in FIG. 1-2. Thus, when a condition of minimum power under a given feed force is sensed by the device v216, the control apparatus 27A will maintain the ECG apparatus at a condition of minimum power drawn by the motor 13 by again suitably varying the potential generated by the source S. The foregoing has assumed a given feed force for simplicity of illustration. However, it will be recognized that in a manner similar to that described above in connection with the apparatus of FIGS. 8-114, vthe signal derived from the value of spindle power may be used in place of working current to control both voltageand feed force.

Likewise for simplicity in illustration, the foregoing has assumed that the desired operating point would be at the actual point of minimum spindle power. It will be understood that in" many instances of commercial usage, the preferred operating condition may be at some point more or less offset from, and on either side of, such point of absolute minimum. This also parallels the situation in connection with FIGS. v8-14 in which for illustrative purposes the operating condition was assumed to be one of maximum working current but wherein an actual operation might be, and within the scope of the invention could be, located ata selected point more or less Oifset therefrom.

The lembodiment illustrated in FIG. 16 is essentially identical to the embodiment illustrated in FIG. 8. However, in this embodiment, a servo 218 is utilized, the output of which has a feed rate detector 219 to sense the rate of rotation of a screw 221 and a feed force sensor 220 to provide proper limits of feed force and to provide a further input signal to theV control 27B. The table 16 is advanced or rretracted-` by an appropriate rotation of the screw member 221: v,The rate signal indicating the rate at which the screw 221 is rotated will be supplied through conductor 222 to the` control apparatus 27B. The control device 27B will be responsive to said rate signal to supply a signal through the conductor 223 to control the rotational speed and direction'of rotation to the servo 218. Thus, if the feed rate is to low, the control apparatus 27B will respond to increase the speed of the servo 218 through a signal sent through the conductor 223, one feed rate being sampled and compared with a subsequent feed rate in the same manner as above described with respect to the shunt current appearing on conductor 31 and the voltage is then adjusted'up or down to maintain the feed rate nearer butto thetleft of the peaks shown in FIG. 2 as associated with feed pressure of |12, 31 and 48 pounds respectively. The electrical system will be precisely the same for this embodiment as that illustrated and described -above for the principalembodiment excepting only that the currentuappearing on conductor 31 will be taken from the-sensor 219 and will be proportional to the feed rate rather than as previously to the working current itself. The feed force sensor 220 will maintain the preferred relationship with the feed rate so that the operating point of the machine will be maintained within a predetermined range similar to that shown in FIGS. 7 and 7A.

While preferably all of the foregoing embodiments have created the timing pulses applied to conductor 42 by senssing the rotation of the grinding wheel spindle, there is no essential reason for relating said pulses to any particular position or speed of operation of said grinding wheel. However, there is an advantage of using the spindle speed asa clock because as` the system becomes more loaded, the grinding device slows down and therefore slows down the pulses to the timing section. This is sometimes desirable to accommodate the sluggish generator response which may occur at high load levels with some types of generators. Nevertheless, any other means for producing such pulses at a reasonably accurate rate will be acceptable provided only they are rapid enough to control the applied voltage in close relationship to the grinding conditions including such variable conditions as changing of the surface area of the workpiece as a result of the grinding operation, and provided further that they are not so rapid as to exceed the capacity of the rest of the equipment to respond thereto.

Further, it will be recognized that if the rotating spindle of the grinding wheel is used to produce the timing pulses, the rate of such pulses may be freely varied by varying the number of magnets or other magnetic or inductive devices used for this purpose on said spindle or, if necessary to accommodate a relatively slowly responding voltage generator. The counter 36 may be arranged to respond only to multiples of pulses such as counts of 2, 4 and 8 instead of as shown to respond to single pulses in counts of l, 2 and 4.

In the foregoing-described embodiment, the apparatus shown is sensitive only to one performance parameter, namely, the amperage of current flowing between the workpiece and the grinding wheel and is adapted to control two control parameters, namely, the voltage provided to supply the working current and the feed force. However, it will be apparent that multiple performance parameters may be sensed and either applied jointly to the input 31 of the analytical section 37 or each of such performance parameters to be sensed may be provided with a separate analytical section whose output is then applied jointly to the logic section 38 and to the table feed device.

Likewise, other relationships of measured or calculated parameters may be utilized for control and/ or reference purpose. For example, instead of sensing the current owing as the reference performance parameter, suitable means may be provided according to known techniques and in View of the foregoing disclosure for sensing the ratios of working current to spindle power, feed rate to spindle power, or feed force to spindle power.

Although a particular embodiment of the invention has been disclosed in detail for illustrative purposes, it will bev recognized that variations or modifications of the disclosed apparatus, including the rearrangement of parts, lie within the scope of the present invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In an electrochemical grinding machine having a rotating metal-bonded grinding device having an endless surface impregnated with essentially nonconudcting abrasive grain, an electrolyte supply for supplying electrolyte between said grinding device and an electrically conductive workpiece and power source means for establish ing a potential difference between said grinding device and said workpiece and establishing a flow of current between said grinding device and said workpiece, the magnitude of said current being proportional to the magnitude of said potential difference and having at least one inlection point therein over the range of variation of said current, apparatus for searching through and maintaining a control of the conditions of an electrochemical grinding operation on said workpiece to maintain an optimum operating condition, comprising in combination:

timing means producing a series of timing pulses foi energizing a plurality of conductors simultaneously in multiple patterns; sampling means connected in circuit with said power source means and responsive to one pattern appearing on said conductors for sampling the value of current applied at a given instant between said workpiece and said grinding device; memory means connected in circuit with said sampling means for remembering the value of said sampled current;

logic means responsive to different patterns on said conductors and operative at a period in time subsequent to said sampling for responding to a previous condition of said apparatus and altering the voltage applied between said grinding device and said workpiece, said logic means being responsive in one direction to signals indicative of an increase in current in response to a selected increase in voltage of one magnitude and responding in an opposite direction to pulsesindicative of an increase in current in a different magnitude resulting from a further selected increase in voltage whereby the response in one direction progressively and stepwise increases the voltage applied to ithe system and in response to signals in the opposite direction, stepwise and progressively decreases the voltage;

comparison means connected in circuit with said memory means and said sampling means for comparing said remembered current and an instantaneous value of current flowing between said grinding device and said workpiece subsequent to said altering and issuing a signal indicative of the relationship between said remembered value and said instantaneous current; and

control means applying said signal to said logic means for further altering the voltage applied between said workpiece and said grinding device as needed to maintain said current flow in a zone encompassing said inflection point.

2. The apparatus defined in claim 1 including pressure control means controlling the pressure at which said workpiece is urged against said grinding device, said pressure control means being responsive to the magnitude of the instantaneous value of current to regulate the magnitude of pressure at which the workpiece is urged against the grinding device simultaneously with the above-mentioned changes in voltage.

3. In an electrochemical grinding machine having a grinding device, an electrolyte supply for supplying electrolyte between said grinding device and an electrically conductive workpiece and power source means for establishing a potential difference between said grinding device and said workpiece, apparatus for automatically searching through and maintaining a control of the conditions of an electrochemical grinding operation on said workpiece to maintain an optimum operating condition,v the combination comprising:

control parameter generating means for generating a variable control parameter to control the electrochemical grinding operation on said workpiece about said optimum operating condition;

performance parameter generating means for generating a varying performance parameter in response to sa-id machining operation, the magnitude of sa-id performance parameter being proportional to the magnitude of said control parameter and having at least one inflection point therein over the range of variation of said performance parameter;

detecting means connected in circuit with said performance parameter generating means for detecting said performance parameter and producing a signal proportional to said performance parameter, said detecting means including first means for sampling and remembering a value indicative of the performance parameter, second means for incrementally varying the control parameter to vary the performance parameter, means for comparing with the remembered value a numerical value indicative of the performance parameter following the varying of the control parameter and issuing said signal indicating the manner, if any, by which said performance parameter has changed; and

control means connected in circuit with said detecting means and responsive to said signal, said control means including interpreting means for detecting a zero differential at said inflection point in said signal, which zero differential defines said optimum condition, said interpreting means interpreting said signal and altering said control parameter in response to said signal for further altering said performance parameter as required for maintaining said performance parameter at said optimum condition.

4. The apparatus of claim 3, including means for generating a second variable control parameter to further control the electrochemical machining operation on said workpiece, said second control parameter also producing said varying performance parameter, the magnitude of which is also proportional to the second control parameter, said first-mentioned control parameter, said second control parameter and said performance parameter, when varied over a given range, defining a contoured surface having at least one peak condition thereon, said control means being responsive to said signal generated by said detecting means to maintain said performance parameter at said peak condition.

5. The apparatus of claim 3, wherein said performance parameter is the working current.

6. The apparatus defined in claim 3, including a motor for moving said grinding device and means for producing a signal proportional to the input power to said motor, and wherein said performance parameter is said input power to said motor.

7. The apparatus defined in claim 3, including means for advancing said workpiece toward said grinding device and means for producing a signal proportional to the rate at which said workpiece is advanced, and wherein said performance parameter is said nate at which said workpiece is advanced toward said grinding device.

8. The apparatus defined in claim 3, wherein a working gap is defined between said workpiece and said grinding device, and wherein said power source means comprises f electrical power generating means connected across said working gap and adapted to cause a working current to flow through said working gap, and wherein said performance parameter is the gap resistance across said working gap- 9. The apparatus defined in claim 3, including a motor for moving said grinding device, wherein said power source means comprises electrical power generating means connected across a working gap between said workpiece and said grinding device and adapted to cause a working current to flow through said working gap, and wherein said performance parameter is the ratio of working current to the input power to the motor.

10. The apparatus defined in claim 3, including a motor for moving said grinding device and means for advancing said workpiece toward said grinding device, and wherein said performance parameter is the ratio of the workpiece feed rate to the input power to the motor driving the grinding device.

11. The apparatus defined in claim 3, including a motor for moving said grinding device and means for advancing said workpiece toward said grinding device, and wherein said performance parameter is the ratio of the workpiece feed force to the input power to the motor driving the grinding device.

12. The apparatus according to claim 3, in which the performance parameter is the working current, wherein said first means samples and remembers the value of the current flowing prior to a predetermined point in time, wherein said second means signals the point in time and thereupon incrementally varies the magnitude of the instantaneous current flowing between the workpiece and the grinding device, wherein said comparing means compares the magnitude of the altered current flowing after the point in time with the value of the remembered current and issues a signal indicating which thereof is greater and, wherein said control means is responsive to the last-named signal for maintaining the working current at said optimum condition.

13. The apparatus according to claim 12, in which said altered current is the instantaneous current flowing after the point in time.

14. The apparatus according to claim 12, in which said altered current isya time integrated sample of the current owing after the point in time.

15. The apparatus according to claim 3, in which the manner includes both the amount of change in' the performance parameter and the direction of such change.

16. The apparatus according to claim 3, wherein said comparing means for indicating the manner of the change of the performance parameter is further adapted to produce a signal indicating both the magnitude of such change and the direction of such change and wherein said interpreting means is vresponsive to the last-named signal for altering the control parameter in one direction if the performance parameterl is changed in one direction and for altering the control parameter in another direction when the change of the performance parameter is in another direction.

17. The apparatus according to claim 3, wherein said interpreting means includes means for altering the control parameter in one direction if the performance parameter changes by a predetermined amount in one direction, for maintaining the control parameter unchanged if the per- Z4 formance parameter changes less than a predetermined amount in each direction and for altering the control parameter in the opposite direction if the performance parameter changes by an amount exceeding a predetermined minimum and in the opposite direction.

References Cited UNITED STATES PATENTS 3,238,675 3/1966 Abbott et al. 204--228 3,288,693 1 1/1966 Livshits 204-225 3,463,720 8/ 1969 Wilkinson et al 204-143 3,409,532 11/1968 Shaw et al. 204--143 3,004,910 10/1961 Keeleric 204--143 2,920,026 1/ 1960 Kistler 204-143 OTHER REFERENCES Keeleric, Steel, pp. 84-86, Mar. 17, 1952.

JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner U.S. Cl. X.R. 

